Fix the brightness corrections for the LowRes Masks

[akgunter]

I assumed the brightness corrections for the regular masks would translate to the hi-res ones. That was probably not inaccurate on previous versions of the lowres masks, but it's definitely incorrect now.

The shadow and grille masks should probably use correction 1.0, and the slot will likely be something like 0.75. I'll run through other shaders and double-check their methods of calculating that.